This study aims to develop a more efficient and timely system for assessing renal function and acute change in renal function. It proposes to determine if any of four commercially available grades of technetium 99mTc-DTPA can be used to provide good estimates of GFR. Clearance results from these four chelates of technetium will be contrasted with a gold standard of inulin clearance to determine the best marker of GFR for clinical use.